As is well known, the present supply of oil is being rapidly depleted. Thus, its use as a source of energy, i.e. a heating fuel in a furnace, is becoming increasingly expensive while the supply is becoming increasingly uncertain. Accordingly, attempts have been made to substitute other types of fuels for oil, such as coal, charcoal, and the like.
However, coal and charcoal, when burned in a natural draft furnace (such as a small unit in an apartment or a boiler for an apartment building) create a great deal of particulate matter, i.e., volatiles, semi-volatiles, gravimetric materials, and the like, which creates air pollution. Accordingly, such use of coal and charcoal has been disparaged. Instead generally the focus with coal and charcoal has been in heavy industry and the power industry.
In heavy industry, the coal was transformed into coke. The coke, and also charcoal, was for use as a reducing agent for iron oxide ores in the manufacture of steel. In the power industry, the coal was burned in some electricity generation plants to generate the electricity. On the other hand, generally the focus with briquettes, compositions of a mineral acting as a binder (such as limestone, i.e., calcium carbonate, or clay, i.e. aluminum silicate, also known as zeolite) admixed with coal, charcoal, and combinations thereof, has been for food-cooking grills or stoves. For instance, there are the American outdoor grill used in the backyard or patio, and the Asian charcoal cook stove, such as the indoor portable hibachi used by the Japanese or the indoor in-ground pit with separator directing air flow to the bottom thereof used by the rural Chinese.
With respect to briquettes for instance, U.S. Pat. No. 4,787,914 to Crace (issued Nov. 29, 1988) involves a briquette wherein clay in a desired predetermined portion is added to charcoal, coal, or a mixture thereof, to achieve a desired flavor enhancement for a food-cooking briquette.
Also of interest is U.S. Pat. No. 2,110,370 to Lum (issued Mar. 8, 1938). This patent involves a composition of bituminous coal and clay that is heated to 350.degree. C., preferably in the absence of oxygen, to produce a product with a decreased clinkering tendency as compared to bituminous coal absent the clay.
Additionally relating to briquettes is U.S. Pat. No. 4,661,119 to Andersson et al. (issued Apr. 28, 1987). This patent involves briquettes suitable for use as an auxiliary fuel for the melting of minerals in the manufacture of mineral wool. The briquettes comprise 30-75% by weight particles of coke fines or coal fines, at least 7% by weight hydraulic cement binder, and at least 15% by weight filler that is an oxidic mineral component chosen from sand (silicon dioxide) or limestone powder (calcium carbonate powder).
Also, it is noted that U.S. Pat. No. 1,875,287 to Weber (issued Aug. 30, 1932) involves a process for preparing semi-coke briquettes from bituminous coal. The process involves preparing a binding agent containing sulphite spent liquor with clay in a colloidal suspension, mixing the binding agent with fine bituminous coal, and forming the mixture into briquettes. The briquettes are then heated to drive off moisture and then subjected to a low temperature carbonization.
Another related patent is U.S. Pat. No. 4,432,771 to Sawyer (issued Feb. 21, 1984). This patent involves an aqueous fuel slurry of 65-70% coal powder, 0.5-5% by weight wetting agent, 0.15-0.8% by weight clay stabilizing composition, and the remainder water. The clay stabilizing composition, when added to the aqueous fuel slurry, provides a stabilizing gel structure for the slurry.
Lastly of background interest is U.S. Pat. No. 136,375 to Hayes (issued Mar. 4, 1873). This patent involves a process of combining calcareous clay and coal waste with boiling water, mixing the resultant under high heat to obtain 8-12% calcareous clay, and then mixing the resultant with asphalt.